MICROBIOLOGY Textbook - 2012

CHAPTER 13. PATHOGENIC MICROORGANISMS

13.2. INFECTION AND ROUTES OF TRANSMISSION

Infection (from Lat. inficio — to contaminate) refers to the invasion of a macroorganism by microorganisms and their subsequent multiplication within it, resulting in an infectious process. A human or animal Organism in a state of infection is termed infected, whereas environmental objects that have been contaminated with pathogens are referred to as polluted or contaminated.

The Development of an infectious process depends on numerous factors: the PATHOGENICITY AND VIRULENCE of the microorganism, its infectious dose, the portal of entry and mode of transmission, the state of the macroorganism and its immune system, as well as environmental conditions.

The physical condition of The Human Body plays a crucial role in the progression of the infectious process. Resistance to pathogenic Bacteria can be lowered by fasting, malnutrition, overwork, hypothermia, and stressful situations.

The infectious process develops through several successive stages:

1) entry of the microbe;

2) incubation period — the time elapsed between infection and the onset of clinical disease manifestations. Depending on The properties of the pathogen, the incubation period may range from several hours to several months or even years;

3) prodromal period — the appearance of the earliest general clinical symptoms that are nonspecific for the given disease (slight fever, headache, malaise, loss of appetite, etc.);

4) clinical period — the manifestation of symptoms most typical of the specific disease (fever curve, rashes, Blood picture, localized lesions, etc.);

5) convalescence period — the stage characterized by the subsiding and disappearance of typical symptoms leading to recovery.

Sources of infection include infected humans and animals that shed pathogenic bacteria into the environment, as well as individuals who have recovered from an infectious disease but continue to harbor the pathogen in their bodies for extended periods (referred to as carriers). Intermediate vectors play a major role in the spread of infectious diseases: insects (mosquitoes, flies, lice, fleas) and certain animals (rats, gophers, dogs, cattle, etc.). The Mechanism of transmission can be realized via three main routes: fecal-oral, airborne (droplet), and contact-based (Direct and Indirect).

The infectious agent may be transmitted through direct or indirect contact with an infected person. Direct transmission of the pathogen from human to human occurs via kissing, handshakes, sexual contact, or blood transfusion from a donor. Pathogenic microorganisms can also be transmitted from sick animals to humans through bites or animal care activities.

In indirect contact, the infection is transmitted via various objects previously handled by the infected individual.

Pathogenic microorganisms are most frequently spread via airborne droplets during speaking, coughing, or sneezing. Mucus droplets released into the air may carry tubercle bacilli, plague bacilli, pneumococci, streptococci, as well as the causative agents of whooping cough, measles, Influenza, smallpox, and other diseases.

Soil also serves as a source of certain pathogenic bacteria. Pathogenic microorganisms enter the soil via feces, animal carcasses, and various domestic refuse. The soil may harbor anthrax bacilli, tetanus spores, gas gangrene, botulism agents, and others. The causative agents of these diseases form spores that can persist in the soil for long periods.

Water plays a significant role in the transmission of infectious diseases. It washes pathogenic microbes from the surface layers of soil and carries them into open and closed bodies of water. The causative agents of cholera, typhoid fever, dysentery, brucellosis, leptospirosis, and various fungal and viral diseases can survive in water for quite a long time.

Food products represent a particular hazard in the spread of infections. Pathogenic agents of many infectious diseases can be transmitted through foodstuffs. The spread of typhoid fever, paratyphoid fever, dysentery, cholera, tuberculosis, and brucellosis is frequently associated with contaminated milk and dairy products. Meat and meat products consumed without proper veterinary and sanitary inspection or adequate heat Treatment can cause anthrax, tuberculosis, brucellosis, FOOT-and-Mouth disease, tularaemia, and Q fever. Fish and fishery products often cause food-borne toxic infections induced by Salmonella, Proteus species, Clostridium perfringens, as well as staphylococcal food poisoning and botulism.

Knowledge of the properties of microbes that cause diseases and food poisoning, along with their routes of entry and conditions for multiplication, is essential for the Prevention of such diseases.